7 public questions tagged with this topic.
A stable population has balanced birth and death rates, leading to minimal overall population change.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Life History Variations and Population Interactions - Overview
In logistic growth, population growth slows as it nears carrying capacity due to resource limitations.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Growth - Exponential and Logistic Models
For a population observed at discrete time intervals, the finite rate of increase is λ = N(t+1)/N(t). A value of 1 means that each census contains the same number of individuals as the preceding census, so abundance is stable rather than rising or falling. Equivalently, births plus immigration exactly balance deaths plus emigration over the interval. This does not imply that no individuals are born or die; demographic turnover may be substantial while net population change remains zero. In an age-structured population, λ = 1 is the long-term result after the stable age distribution has been reached, even though particular age classes may temporarily change in size. Values above 1 indicate multiplication, whereas values below 1 indicate decline. The corresponding continuous intrinsic rate is r = ln λ, making λ = 1 equivalent to r = 0. Stability also refers to expected size under the model; environmental and demographic stochasticity can still produce fluctuations around that expectation.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 11
“Less extinction prone” for an organism with low variability in population size is. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. The mechanism should be evaluated across both local and global scales. Local disappearance can be reversed by recolonization, whereas global extinction is irreversible and requires the loss of every surviving population. The remaining alternatives—“Highly extinction prone”, “Genetically unstable”, “Unable to adapt”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Human-driven habitat conversion, exploitation, introduced enemies, pollution, and climate change often interact rather than acting independently. Traits such as slow reproduction or ecological specialization can magnify vulnerability. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates. The cited framing is therefore most useful when treated as a conditional biological claim, with assumptions about scale and environmental context kept explicit.
Ref: Conservation Biology, Primack & Sher, 6th Ed., Ch. 7
“Population is stable” for the value of r₀ = 1 implies. This relationship follows from the ecological mechanism represented by the terms in the item, not merely from an association between their names. Life-history traits reflect allocation among growth, maintenance, survival, and reproduction. Energy invested in many offspring cannot simultaneously be invested in large offspring, prolonged care, or future breeding, creating measurable trade-offs. The remaining alternatives—“Population is increasing”, “Population is declining”, “Net migration is zero”—refer to different states, processes, or scales and therefore do not express the same causal relationship. Survivorship curves summarize age-specific mortality: Type I concentrates loss late in life, Type II approximates a constant hazard, and Type III concentrates loss early. They are empirical patterns, not rigid taxonomic rules. This distinction matters because similar surface patterns can arise through different mechanisms, whereas ecological prediction depends on identifying the mechanism that actually changes rates.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 10
Alternative prey with uncorrelated abundance do not generally lead to unstable equilibrium. They can buffer a generalist predator’s food supply because one prey may be abundant when another is scarce, and predator switching toward common prey can stabilize dynamics. They can also generate apparent competition or sustain predators that overexploit a rare prey, so the outcome depends on functional responses, switching, and interaction strengths; uncorrelated abundance alone has no fixed destabilizing sign. Predator saturation, by contrast, is a recognized destabilizing mechanism in many predator–prey models. With a saturating type II functional response, predation fails to increase proportionally at high prey density, allowing prey outbreaks, while continued predation at lower densities can deepen crashes. Stability must be evaluated from specified equations or Jacobian eigenvalues, not assigned from a single qualitative feature. Mimicry and dormancy may alter encounter rates or temporal structure but are not universal determinants either. KEY MISMATCH: the keyed alternative-prey statement is not generally valid, and predator saturation is the better-supported destabilizing factor among the choices.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14
A predator with multiple prey can persist by switching toward whichever prey is relatively abundant, reducing pressure on a prey species when it becomes rare. This frequency-dependent switching can provide each prey a low-density refuge and dampen extreme consumer–resource cycles. A broader resource base also prevents immediate predator starvation when one prey declines, although persistent predator subsidy can instead create apparent competition and harm a rare focal prey. Stability therefore depends on switching strength, functional responses, and whether prey fluctuations are synchronized. Rapid prey reproduction alone does not guarantee coexistence; it may support recovery, but delayed density dependence can amplify oscillations. Lack of predator territory has no consistently stabilizing effect, and isolated prey may escape predation locally but do not by themselves establish dynamical coexistence. Among the alternatives, multiple prey provide the clearest mechanism for buffering food availability and distributing predation. The conclusion is conditional rather than universal: generalist predators stabilize coexistence most effectively when they preferentially attack common prey instead of maintaining heavy pressure on a declining species.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 14
